1 Field of the Invention
This invention relates to a telephone apparatus comprising a fixed station connected to a telephone line and a telephone handset, the handset being mobile and detachable with respect to the station.
2 Description of the Prior Art
Such a telephone apparatus is used as a public telephone, with a view of remedying main disadvantages of public telephones based on charge prepayment by coins or magnetic, holographic or memory card. The disadvantages are chiefly those connected
with maltreatment of mechanical parts such as dial or keypad and telephone handset,
with the possibility of blocking the coin or card slots such as to prevent prepayment for the telephone communication, and
with the management of the money received, requiring the presence of coin container in the apparatus and periodic collection thereof when telephone communications are paid for in coins, or the sale of prepayment credit cards by special distributors when telephone communications are prepaid by card.
In a public telephone apparatus of the type defined above, for example as described in French Patent Application No. 2 538 978, a high frequency modulation circuit and a high frequency demodulation circuit included in the fixed station are respectively linkable to a high frequency demodulation circuit and a high frequency modulation circuit included in the handset through a bidirectional infrared link to transfer digital voice and tone signals between the station and the handset. Apart from the inconvenience to the user of having to keep his handset pointed towards two opto-electronic transducers embedded in the ceiling of a telephone booth containing the fixed station, throughout the duration of a telephone call, the infrared link may be disturbed either by a cutoff due to the passage of a foreign body or by movement of the handset, which interrupts the call in progress. Furthermore, the handset has a stand and power supply circuit, such as batteries, and the opto-electronic transducers contribute to an increase in the cost of the handset and the fixed terminal.